The present invention relates to an apparatus for spin polarizing a particle beam, adapted to process an input particle beam in such a way as to generate an at least partially spin polarized output particle beam.
It is known that the generation of spin polarized electron beams is at present very difficult and ineffective in terms of brightness and stability, and is therefore difficult to use in practical applications.
The polarization of electrons has been considered for many years to be an impossible task, mainly owing to the failure of methods based on classical mechanics, such as the Stern-Gerlach experiment for ions [1]. The first methods for producing weakly polarized beams consisted in the use of the asymmetries induced by the spin-orbit coupling in the Mott scattering on a gold foil [1].
At present, a high polarization is obtained mainly with semiconductor photocathodes, mainly multilayer GaAsP/GaAs structures under stress which are grown on GaP [2]. The mechanical stress in the semiconductor produces splitting in the valence bands, which promotes electron transitions with a well-defined polarization. The light from a laser is diffused on the photocathode to produce a localized emission of polarized electrons, which are thus accelerated to the working conditions.
The known polarized sources may achieve a brightness of 107 A cm−2 sr−1 and a polarization purity of up to 90% [3]. Whereas for some applications these values may be sufficient, it should be noted that the effective dimensions of the source are of the order of several hundred nanometers, and that the lifetime under DC operation may reach at most 36 hours [3].
An article has recently proposed a method for the spin polarization of an electron beam in which the diffraction of the electrons is utilized [4]. However, this publication proposes fields and/or lateral dimensions for the apparatus which do not appear to be obtainable under normal laboratory conditions.